The cable-style online TV service Hulu is developing could be a focus for media investors this quarter, but it is unlikely to pose a serious threat to cable

A new TV service in the works from Hulu could give media companies the power to wage war against their pay-TV distributors. But they have ample reason to want to keep the peace.

As the companies report earnings in the coming weeks, investors will be looking for details on the cable-style online TV service Hulu aims to launch in the first quarter of 2017. The theory is that Hulu, owned by Walt Disney, 21st Century Fox and Comcast’s NBCUniversal, should be able to offer a more robust content lineup for a lower price than...